Large and small caliber guns used in combat vehicles present considerable problems in the harmful effects on personnel of propellant gases expelled from the open breech or receiver into the interior of the vehicle during firing of the weapon.
Prior art methods employed to overcome these effects include systems relying on the direct application of a portion of the propellant gases to clear the bore of propellant gases through the muzzle. In one such system, valves control flow of a portion of propellant gases through holes in the gun barrel into and out of an accumulator which are used to expell propellant gases through the muzzle. Sequencing of the valve operation is pressure actuated presenting considerable design problems.
In another type prior art bore evacuation system, an external source of auxiliary ejection gas is employed which also involves direct application of the ejection gas to the propellant gases. In this system, the breech must be opened before the ejection gas can be introduced into the bore thereby permitting some evacuation of propellant gases through the breech. These types of systems are thus particularly not suitable for automatic weapons because of manufacturing design problems and vehicle interior space limitations.